During a semiconductor fabrication process, integrated circuits are formed on a wafer. The wafer is a semiconductor substrate made of silicon or gallium arsenide. The wafer contains a plurality of chips. These chips are designed with different circuits for various functions, such as microprocessor, memory circuits and logic circuits. After the fabrication process and before it is singulated, the wafer will need to pass functional test to verify their electrical performance within design specification. Conventionally, a test head of a tester for chip probing usually mounts a probe card with a plurality of probe needles or other contact members for contacting with electrodes, such as bonding pads or bumps, of a wafer. The probe card provides temporarily electrical transmission between the tester and the wafer under test. As new semiconductor products varies from generations to generations, the conventional probe card will also need to be modified and redesigned.
A conventional modular probe head assembly is disclosed in the ROC Taiwan Patent publication No. 547,643. As shown in FIG. 1, the probe card includes a printed circuit board 10, a probe head 20, a flexible printed circuit board 30, and a pressure plate 40. The probe head 20 includes a silicon substrate 21 which is installed in a holder 22. The silicon substrate 21 has an upper surface and a lower surface, wherein the upper surface is arranged with a plurality of probe pads 23, conductive circuits and contact pads 24 at the periphery. The conductive circuits provide electrical connection between probe pads 23 and contact pads 24. The pressure plate 40 is formed with at least an opening corresponding in location to silicon substrate 21. The pressure plate 40 presses the flexible printed circuit board 30 to acquire electrical contact between the contact terminal 31 and the contact pads 24 of the silicon substrate 21. Nevertheless, if the probe head 20 and flexible printed circuit board are mal-alignment, it is unable to provide electrical connection between the contact terminal 31 of flexible printed circuit board 30 and the contact pads 24 of the probe head 20 by compression of the pressure plate 40. Furthermore, the pressure plate 40 and the flexible printed circuit board 30 provides a certain height above the probe head 20 so that a long probe needles 25 are required to fabricated on the probe pads 23 to contact with the wafer under test for chip probing.